1. Field
This disclosure relates to a cooling system that cools a secondary battery for driving a vehicle.
2. Description of Related Art
In an electric vehicle, such as a hybrid vehicle or an electric-powered vehicle, a secondary battery (battery) that stores electric energy for driving the vehicle is installed. Since the secondary battery has internal resistance, and its temperature rises due to charging or discharging, it is necessary to cool the secondary battery. Thus, it has been proposed to provide a cooling fan around the secondary battery, and forcedly cool the secondary battery by air, using the cooling fan.
For example, a cooling system for vehicular electric components in which a cooling fan is provided in the vicinity of a secondary battery is disclosed in Japanese Patent Application Publication No. 2010-158964 (JP 2010-158964 A). In the system of JP 2010-158964 A, a duct in which cooling air produced by driving of the cooling fan flows diverges midway in two directions, so as to allow switching of channels of the cooling air, according to the temperature of a charger installed on the vehicle. In this cooling system, a command duty of the cooling fan is changed according to the temperatures of high-voltage secondary battery and vehicle-mounted charger to be cooled. The cooling system also detects the presence or absence of a fault of the cooling fan. If a fault is detected, the cooling system outputs the detection result to a diagnostic system, and changes control of the electric components according to the content of the fault.
The presence or absence of an abnormality in the cooling fan is often determined based on detected parameters, such as the actual rotational speed of the cooling fan. Thus, the presence or absence of an abnormality is desirably determined in a steady state in which the cooling fan is stably driven. This is because, if the drive status (such as the fan rotational speed) of the cooling fan varies largely, errors caused by control delay, or the like, may be included in the detected parameters, and the accuracy in detection of a fault cannot be kept sufficiently high.
The cooling system of JP 2010-158964 A, in which the command duty is changed according to the temperatures of the high-voltage secondary battery and the charger, is unlikely to be placed in a steady state; therefore, it is difficult to accurately determine the presence or absence of an abnormality in the cooling fan. Thus, it may be considered to drive the cooling fan at a fixed duty (fixed rotational speed), without changing the command duty (command rotational speed) of the cooling fan. In this case, the drive status of the cooling fan is stabilized, and therefore, the presence or absence of an abnormality can be accurately determined. However, if the cooling fan is constantly driven at the fixed duty (fixed rotational speed), irrespective of the status of the secondary battery and traveling conditions, the secondary battery may not be sufficiently cooled because of insufficient rotational speed, and may be deteriorated, or, conversely, unnecessarily high rotational speed of the cooling fan may result in unnecessary noise and electric power consumption.